In recent years, virtual machine (VM) techniques have been drawing attention. A “virtual machine technique” is a technique by which the hardware resources in one computer are logically divided, and the computer virtually functions as a plurality of independent computers (virtual machines). As the functions of virtual machines are realized with a single computer in this manner, the single computer can be shared among a plurality of users.
In most cases, the hardware resources used and/or necessary for a process are allocated every time a virtual machine performs a process in such a computer. However, there is a limit to the hardware resources that can be retained by a computer, and therefore, the amount of hardware resources to be allocated varies among the virtual machines of users, depending on the usage states of the virtual machines. If there is a virtual machine performing a process with a large processing load, sufficient hardware resources cannot be allocated to the other virtual machines. In such a situation, the virtual machine performing the process with a large processing load might affect the usage environments of the other virtual machines, and the operability of the other virtual machines might become lower.
In view of the above, a system has been suggested to reconfigure the allocation of hardware resources to virtual machines when differences are seen among the amounts of hardware resources allocated to the respective virtual machines (see Japanese Laid-open Patent Publication No. 2002-202959 and Japanese Patent No. 4,018,900, for example).